1. Field of the Invention
The present invention relates to an injector that is disposed in an internal combustion engine to inject fuel, which serves for combustion, through a nozzle hole.
2. Description of Related Art
In order to accurately control output torque and a state of emissions of an internal combustion engine, it is important to accurately control a state of fuel injection, such as injection start time and injection quantity of fuel injected from an injector. Accordingly, a technology for detecting an actual state of injection by detecting pressure of fuel that varies with the injection is conventionally proposed. For example, actual injection start time is detected by detecting the start time of decrease of fuel pressure in accordance with the injection start, and actual injection completion time is detected by detecting time for the stop of increase of fuel pressure in accordance with completion of the injection (e.g., JP-A-2008-144749 corresponding to US2008/0228374A1; JP-A-2009-057926 corresponding to US2009/0056676A1: JP-A-2009-057927 corresponding to US2009/0063011A1).
In detecting such a fluctuation of fuel pressure, the fluctuation of fuel pressure caused due to the injection is buffered in the common rail using a fuel pressure sensor (rail pressure sensor) that is disposed directly in a common rail (pressure accumulation container). Therefore, accurate fluctuation of fuel pressure cannot be detected. For this reason, the inventions described in JP-A-2008-144749, JP-A-2009-057926, and JP-A-2009-057927 aim to detect the fuel pressure fluctuation before the fuel pressure fluctuation due to the injection is buffered in a common rail, by disposing a fuel pressure sensor in an injector.
However, although the disposition of the fuel pressure sensor in the injector is described, details of its arrangement position are not described in the above-cited publications JP-A-2008-144749, JP-A-2009-057926, or JP-A-2009-057927. Accordingly, as illustrated in FIG. 6, the present inventors have studied structure of an injector for disposing a fuel pressure sensor 80x. 
More specifically, the injector is configured to include a main body 40x having a supply port 421ax for high pressure fuel on an outer peripheral surface of its cylinder, and the fuel pressure sensor 80x attached to the main body 40x. A high pressure passage (first passage 421x and second passage 422x) through which high pressure fuel flows from the supply port 421ax toward a nozzle hole (not shown), and a sensor passage 46x which branches from the first passage 421x to guide high pressure fuel to the fuel pressure sensor 80x, are formed by drilling inside the main body 40x. 
The first passage 421x extends from the supply port 421ax toward a central portion of the main body 40x, and the second passage 422x extends from a downstream end of the first passage 421x toward the nozzle hole. The sensor passage 46x branches from halfway along the first passage 421x. 
Nevertheless, by using the above-described structure in which the sensor passage 46x branches from a halfway portion of the first passage 421x, working man-hours for passages increase because of the addition of the sensor passage 46x to the first passage 421x and the second passage 422x. Furthermore, since the sensor passage 46x branches from halfway along the first passage 421x, a branching portion (i.e., regions indicated by numerals y1, y2 in FIG. 6), in which stress by the high pressure fuel is concentrated, increases, so that pressure resistance inside the main body 40x against the high pressure fuel is reduced.
In view of this problem, the present inventors have examined branching of the sensor passage 460x (see an alternate long and short dash line in FIG. 6) from the downstream end of the first passage 421x toward the opposite side from the second passage 422x. As a result of this examination, the sensor passage 460x is drilled in the main body 40x at one time along with the second passage 422x, so that increase of working man-hours is avoided. Moreover, the stress concentration region y2 is eliminated, and the pressure resistance inside the main body 40x is thereby improved.
However, on the other hand, when forming the second passage 422x and the sensor passage 460x at one time, the forming length (see L1 in FIG. 6) is made great. Therefore, it is made difficult to accurately couple an upper end portion of the sensor passage 460x to a communicating passage 461x that communicates between a predetermined portion of the fuel pressure sensor 80x and the sensor passage 460x. Accordingly, high precision is required to form the second passage 422x and the sensor passage 46x. 